Various display devices have been actively researched and developed in recent years. In particular, much attention is paid to organic electroluminescence (EL) devices capable of emitting light with a high luminance by applying low voltage. For example, a light-emitting device comprising organic thin layers formed by vapor-depositing organic compounds is disclosed in Applied Physics Letters, 51, 913 (1987). This light-emitting device has a laminate structure in which an electron-transporting material of tris(8-hydroxyquinolinato) aluminum complex (Alq) and a hole-transporting material of an amine compound are disposed between electrodes, thereby exhibiting more excellent light-emitting properties than those of conventional light-emitting devices having single-layer structures.
Applications of the organic EL devices to color display devices or white light sources have been actively studied in recent years. Light-emitting properties concerning each of blue, green and red lights should be improved to produce a high-performance color display device or white light source. Known as a light-emitting device with improved light-emitting properties is a green light-emitting device disclosed in Applied Physics Letters, 75, 4 (1999), which uses a particular ortho-metalated iridium complex, Ir(ppy)3 (Tris-Ortho-Metalated Complex of Iridium (III) with 2-Phenylpyridine). This green light-emitting device exhibits a high external quantum efficiency of 8%, which exceeds limit of external quantum efficiency of conventional light-emitting devices, 5%. However, the green light-emitting device using Ir(ppy)3 emits only a green light to have a narrow applicability as a display device. Thus, expectations are high for the development of a light-emitting device that can emit light of the other color with high efficiency. Turning to the blue light-emitting devices, though many devices using distyrylarylene or a derivative thereof such as DPVBi (4,4′-bis(2,2′-diphenylvinyl)-biphenyl) have been proposed, the upper limit of the external quantum efficiency has been 5%. Development of the blue light-emitting device exhibiting the external quantum efficiency exceeding 5% has been highly expected because it will contribute for the progress of the color organic EL device and the white light-emitting device excellent in the efficiency.